This invention relates to an improvement of a pump apparatus used as a hydraulic source of a steering apparatus of a vehicle.
U.S. Pat. No. 6,845,310 (corresponding to Japanese Patent Application Publication No. 2003-285748) discloses a conventional pump apparatus that a steering apparatus for a vehicle employs. This pump apparatus is configured to determine a basic current command value based on a current command value according to a steering angle sensed by a steering angle sensor, a current command value according to a steering angular speed calculated based on the steering angle, and a current command value according to a vehicle speed sensed by a vehicle speed sensor, to add a standby current command value to this basic current command value, and to output the summation of the standby current command value and the basic current command value as a solenoid current command value. A standby flow rate based on the standby current command value is always ensured. With this, it is possible to prevent seizure of the steering apparatus, and to improve responsiveness of the steering apparatus. Moreover, it is possible to oppose the disturbance such as kickback and self aligning torque.